Oxide Film Forming Method
The description of the prior art is provided with reference to a silicon substrate as a substrate body.
As one of the methods of forming an oxide film on a surface of a silicon substrate, the so-called thermal oxidizing method has been known.
In this method, after a natural oxide film is removed by contacting a silicon substrate with fluoric acid solution. The silicon substrate is then cleaned with ultra pure water and dried and the silicon substrate is then contacted with dry oxygen or dry oxygen mixed with an inert gas to form an oxide film.
In this method, however, during the process of heating a silicon substrate from room temperature to a specified temperature which is required for oxidization, for instance, a temperature in the range of 800.degree. C. to 1000.degree. C., an oxide film having a thickness, for instance, from 1.5 to 3.5 nm is formed. The oxide film formed in the heating process is not fine. For this reason, a problem of this prior art method is that, since the thickness percentage of the oxide film which is formed prior to the time when the silicon substrate is heated to the specified temperature is high as compared with the total thickness of the oxide film which is formed upon the completion of all processing steps, an excellent oxide film having insulating capability is not formed. A description is given hereinafter of an oxide film having a high insulating capability with reference to a method of forming a MOSLSI oxide film.
Progress in the field of LSI technology is very rapid, and a DRAM having a storage capacity of 4M bit or more has been put into practical use. In order to manufacture such a high performance electronic device, namely a device having a ultra high degree of integrity, a high performance manufacturing process with high controllability Little affected by uncertain factors is required. As an example of the high performance manufacturing process, the ultra clean process has been known.
For instance, cleaning the process atmosphere is required for forming an oxide film only at a specified temperature by suppressing formation of an oxide film while the silicon substrate is being heated for the purpose to form an oxide film having a high insulating capability. Namely an inert gas or a bulk gas atmosphere with moisture or without oxygen therein is required.
Also cleaning the process atmosphere is required to reduce impurities which were taken into an oxide film when the oxide film is being formed for reducing a lap density in the oxide film and on an interface between the oxide film and the silicon as well as to realize an electrically stable semiconductor device.
As described above, cleaning the process atmosphere is indispensable for realization of an ultra fine LSI.
It is an object of the present invention to provide an oxide film forming method for enabling formation of an oxide film having a high insulating capability on a surface of a substrate body.